ltc1709-7 Linear Technology Corporation, ltc1709-7 Datasheet - Page 26

• Manufacturer Part Number: ltc1709-7
• Description: 2-phase, 5-bit Vid, Current Mode, High Efficiency, Synchronous Step-down Switching Regulator
• Manufacturer: Linear Technology Corporation

LTC1709-7
APPLICATIO S I FOR ATIO
26
SW V
I
COUT
I
CIN
Figure 11. Single and 2-Phase Current Waveforms
R
IN
V
SINGLE PHASE
IN
C
IN
BOLD LINES INDICATE
HIGH, SWITCHING
CURRENT LINES.
KEEP LINES TO A
MINIMUM LENGTH.
+
U
Figure 10. Instantaneous Current Path Flow in a Multiple Phase Switching Regulator
U
SW1 V
SW2 V
I
COUT
I
CIN
I
I
L1
L2
W
DUAL PHASE
SW1
SW2
U
D1
D2
RIPPLE
17097 F11
how to calculate RMS current for the single stage switch-
ing regulator. Figures 3 and 4 illustrate how the input and
output currents are reduced by using an additional phase.
The input current peaks drop in half and the frequency is
doubled for this 2-phase converter. The input capacity
requirement is thus reduced theoretically by a factor of
four! Ceramic input capacitors with their unbeatably low
ESR characteristics can be used.
Figure 4 illustrates the RMS input current drawn from the
input capacitance vs the duty cycle as determined by the
ratio of input and output voltage. The peak input RMS
current level of the single phase system is reduced by 50%
in a 2-phase solution due to the current splitting between
the two stages.
L1
L2
R
R
SENSE1
SENSE2
17097 F10
+
C
V
OUT
OUT
R
L